Good point Naj about the Black paint. Everything was brush painted satin black and for maximum correctness you don't want to mask things off, but rather leave rough edges and even brush strokes per your own taste. Do a search on this site for details and don't forget the edges of the under body before the rocker covers go on....
The very least in the front is all portions that are body colored and will be visible from the front or at a slight angle, through the grill opening. Even the front transverse frame member was sometimes painted black around the bumper mounted air conditioning condenser.
I'd say one of the first things to do after the sub frames, axles and brakes and brake lines, would be installing the heater core. Don't forget to install the throttle linkage along the firewall very early on too. Before the engine goes in, have the complete exhaust system roughly in position. I find it safer to install the engine without the alternator and transmission on a new paint job. This should get you started? ;-)
Good Luck, Tom